Re: [PATCH v2 3/4] perf-report: add --max-stack option to limit callchain stack scan

[David Ahern <dsahern@gmail.com>]

On 10/18/13 8:38 AM, Waiman Long wrote:
> When callgraph data was included in the perf data file, it may take a
> long time to scan all those data and merge them together especially
> if the stored callchains are long and the perf data file itself is
> large, like a Gbyte or so.
>
> The callchain stack is currently limited to PERF_MAX_STACK_DEPTH (127).
> This is a large value. Usually the callgraph data that developers are
> most interested in are the first few levels, the rests are usually
> not looked at.
>
> This patch adds a new --max-stack option to perf-report to limit the
> depth of callchain stack data to look at to reduce the time it takes
> for perf-report to finish its processing. It trades the presence of
> trailing stack information with faster speed.
>
> The following table shows the elapsed time of doing perf-report on a
> perf.data file of size 985,531,828 bytes.
>
> --max_stack	Elapsed Time	Output data size
> -----------	------------	----------------
> not set		   88.0s	124,422,651
> 64		   87.5s	116,303,213
> 32		   87.2s	112,023,804
> 16		   86.6s	 94,326,380
> 8		   59.9s	 33,697,248
> 4		   40.7s	 10,116,637
> -g none		   27.1s	  2,555,810
>
> Signed-off-by: Waiman Long <Waiman.Long@hp.com>
> ---
>   tools/perf/Documentation/perf-report.txt |    8 ++++++++
>   tools/perf/builtin-report.c              |   22 +++++++++++++++++-----
>   tools/perf/builtin-top.c                 |    3 ++-
>   tools/perf/util/machine.c                |   14 +++++++++-----
>   tools/perf/util/machine.h                |    3 ++-
>   tools/perf/util/session.c                |    3 ++-
>   6 files changed, 40 insertions(+), 13 deletions(-)
>

Looks good to me. Acked-by: David Ahern <dsahern@gmail.com>